1. Field of the Invention
The present invention relates to a laser scanning apparatus suitably used in an image forming apparatus adopting an electrophotographic process, such as a copying machine or a printer.
2. Related Background Art
FIGS. 7A and 7B show an example of a structure of a laser scanning apparatus used in an image forming apparatus such as a copying machine or a printer.
FIGS. 7A and 7B are perspective views of the same laser scanning apparatus as viewed from an upper side and a lower side, respectively.
In FIG. 7A, laser beams outgoing from a laser device 10 as a light source pass through a collimator lens 11 to be converted into parallel beams. The parallel beams are converted into band-shaped beams extending in a main-scanning direction by a cylindrical lens 12. After that, the beams are reflected by a first folding mirror 13 and then deflected by a (rotary) polygon mirror 14. After that, the beams are caused to pass through fxcex8 lenses 15 and 16, then reflected to bend toward a lower surface of the apparatus by a second folding mirror 17, and focused into an image on a photosensitive drum (not shown) through a third folding mirror 18, a toric lens 19, and a fourth folding mirror 20. To elaborate, the fxcex8 lenses 15 and 16, the second folding mirror 17, the third folding mirror 18, the toric lens 19, and the fourth folding mirror 20 constitute an imaging optical system for focusing the laser beam into an image on the photosensitive drum. In this case, a photosensitive drum surface is scanned with the laser beam at a constant speed by the action of the fxcex8 lenses 15 and 16. Those parts are mounted to a scanner case 2.
In general, any side of the scanner case 2 is widely opened, to which optical parts or components such as a polygon motor are incorporated. However, if it is left open, dust, toner, etc. are likely to adhere on the optical parts such as the mirror and the lens, thereby remarkably deteriorating optical performances. As a result, a satisfactory image cannot be formed. To cope with this, the parts are mounted thereto, after which the open side is covered with a cover member to keep the inside of the laser scanning apparatus airtight. To be specific, for the laser scanning apparatus having the structure as shown in FIGS. 7A and 7B, in which the parts are mounted to a case member from the upper and lower sides thereof, the upper and lower sides of the apparatus are both opened. Therefore, the cover members should be provided on both the sides of the scanning apparatus.
FIG. 8 shows an upper cover 3 and a lower cover 4 corresponding to both the open sides of the laser scanning apparatus of FIGS. 7A and 7B. For the cover member in a thin plate shape, a resin material or a metal material such as a steel plate can be generally used. However, if the cover member is large to some extent, the member made of the resin material easily deforms such as warping and hardly ensures the strength. Therefore, in many cases, the member is formed of the metal material such as a steel plate. The steel plate is a relatively low-cost material.
The laser scanning apparatus using the metal cover member has, of course, an advantage in that part accuracy such as flatness, a strength, etc. can be secured with ease and the cost is relatively low. On the other hand, however, the following problems are entailed.
In the laser scanning apparatus, when combining a resin scanner case with the metal cover member, a potential difference between the metal cover member and the scanner case develops. Unless being well grounded, the cover member may serve as an antenna for radiation noise generated from the laser scanning apparatus itself, for example, a drive substrate of a laser driver 21, a polygon motor driver 22, a BD sensor (not shown), etc. and a wire harness extending from the substrate or for radiation noise generated from an image forming apparatus main body to further amplify the noise, thereby affecting the image forming apparatus itself or peripheral electric devices, for example, causing a malfunction. From the very beginning, in the case of not attenuating the radiation noise, it is difficult to meet the standards for the radiation noise in countries, which are stipulated for the image forming apparatus.
Japanese Patent Application Laid-Open No. H9-236770 discloses an example of a measure to solve the foregoing problem of the radiation noise generated when the metal cover of the laser scanning apparatus is not well grounded.
Proposed in Japanese Patent Application Laid-Open No. H9-236770 is a laser scanning apparatus equipped with a polygon motor, a scanner case, an imaging optical system, and a metal cover, in which part of the cover member is grounded through a support part of the scanner case, and a ferrite core is further provided to the support part of the scanner case for reducing the radiation noise.
However, the proposal in Japanese Patent Application Laid-Open No. H9-236770 is made entirely on the assumption that the metal cover is provided only on the upper surface of a laser scanning apparatus unit. Therefore, if the same measure is attempted to apply to the laser scanning unit equipped with the metal covers for the upper side and the lower side (upper cover and lower cover) as mentioned in the conventional case, the upper cover and the lower cover respectively need to be grounded to the support part of the laser scanning apparatus. As a result, a cover shape and a frame structure are complicated. Also, installing the ferrite cores for both the covers requires a space, which is undesirable in terms of cost.
Also, it is conceivable that ground wires are connected to the upper and lower covers to ground the covers to the frame etc. of the image forming apparatus main body. In this case, however, for grounding them sufficiently enough to attenuate the noise, the ground wires are connected at the positions twice as many as those of the one-side cover. Thus, easiness of assembly and serviceability are largely impaired.
In addition, the resin scanner case is generally inferior to the metal case such as an aluminum case in mechanical strength and is thus unresistant to vibrations etc., leading to the deteriorated image quality.
The present invention has been made in view of the above-mentioned problem and has an object to provide a laser scanning apparatus capable of preventing occurrence of electromagnetic noise.
Another object of the present invention is to provide a laser scanning apparatus capable of grounding a conductive cover member for preventing the occurrence of the electromagnetic noise.
Still another object of the present invention is to provide a laser scanning apparatus, including: a laser light source; a rotary polygon mirror for deflecting a laser beam emitted from the laser light source for scanning; an imaging optical system for focusing the laser beam deflected by the rotary polygon mirror into an image; a containing member for containing the rotary polygon mirror and the imaging optical system; a first conductive cover member for closing a first opening portion of the containing member; a second conductive cover member for closing a second opening portion of the containing member; and conductive connection members for electrically connecting between the first conductive cover member and the second conductive cover member.
Other objects of the present invention will be apparent upon reading the following description taken in conjunction with the accompanying drawings.